It has long been desired to construct water tight plug connectors for electric cables so as to provide a proper seal against access of water when the cable is submerged in deep water. However, serious difficulties have been encountered.
When the connectors are constructed for plugging-in only above the water, it is usual to seal the connector members by elastic gaskets against the entrance of water into the electric contact area in order to avoid grounding and short-circuiting of the contact members by any entering water. These elastic gaskets necessarily are water tight only up to a certain pressure of the surrounding water. They fail when the external water pressure overcomes the mechanical pressure which acts on the sealing gasket. Such plug connectors are therefore useful only down to limited depths of the water.
Other plug connectors are built to allow plugging in under water. Usually the insulating parts of such connectors are constructed in certain shapes and of certain materials so as to disrupt the film of water which otherwise would establish an electrically conductive connection between the surrounding water and the electric contact members. By such constructions, the plugged in connector has sufficient insulative resistance between the surrounding water and any water contained in the contact region of the plug connector. At least one of the insulating parts of such connectors is usually made of an elastic material, the elasticity of which is utilized for disrupting the aforementioned film of water.
It is a disadvantage of connectors of this latter type that continued use of the cable and repeated opening and closing of the plug connections lead to failure by fatigue of the elastic material. The resulting reduction in elastic force of this material makes this material unable to disrupt the water film during and after a new plugging-in process. It has been an additional essential drawback of such connectors, made of elastomeric material, that they could be connected only with cables insulated by elastomeric material, which is not very effective as an electric insulator.
Cable connectors for underwater plugging-in have also been proposed in certain forms designed to displace the water from the contact region during the plugging-in process. These require expensive constructions for the contact carriers with special apertures for escape of water displaced from the contact region. These constructions also require a considerable length of the contact carriers to prevent the entrance of surrounding water after the plugging-in, and they do not provide adequate contact pressure between contact members.